The present invention relates to a method and apparatus for the formation of shells to close the ends of metal cans and, more particularly, to a method and apparatus for forming shells for can ends at two stations contained within the same press and for transferring the shells between the stations.
One common way of packaging liquids such as soft drinks, beer, juices and the like, is within cans typically formed from aluminum. In such cans, a unitary or deep drawn can body is usually manufactured to include the can side walls, as well as an integral bottom. Other cans may have a coated metal seamed body, with a separate attached bottom which might be in the form of a shell such as is used for forming a can top, as is described further below. In either event, the upper end, which includes the means by which the can is later opened, is manufactured separately and attached to the can body after the can has been filled. These so-called easy-open or "pop-top" ends are made from a shell which is converted to an end by appropriate scoring and attachment of a pull tab by integral riveting techniques. The shells are manufactured from sheet metal by severing a suitable blank from a strip of stock material, forming the blank to define a central panel, surrounded by a reinforcing countersink and chuckwall configuration and a shell curl which is designed to interact with a body curl of a can during sealing of the can. The blank may be of the type disclosed and claimed in commonly assigned U.S. Pat. No. 4,637,961.
The shells may be formed in a two-stage operation in which a shell preform is formed at a first station and the preform is transferred to a second station where it is subsequently reformed into a completed shell. In known methods of shell production, a blank is removed from a strip of stock material wherein the shell preform is formed in a first stroke of the press ram and the shell preform is reformed into a completed shell at the second station in a subsequent stroke of the press ram.
A transfer system is provided for transferring the shells from the first to the second station during opening of the tooling in the press. In one approach, the shell preform formed within the first tooling station is vertically positioned for transfer and a device is actuated to strike the shell with an edgewise blow that propels it outwardly from the tooling. Alternatively, a shell which is positioned for transfer may be struck from the side by a stream of pressurized gas issuing from an orifice positioned adjacent to the shell.
Examples of these types of transfer systems may be seen in U.S. Pat. Nos. 4,561,280 and 4,770,022. In these patents, when the actuator or gas stream strikes the shell, the shell is caused to move along the transfer path. Ideally, the shell moves in free flight without contacting any portions of a restraining structure defining the path until the shell is captured at the second station. In addition, a cushion of air may be provided along the lower portion of the shell path in order to minimize contact between the shell and the surface in the tooling defining the transfer path.
Various tool lay-out modifications for the first and second tooling stations are disclosed in U.S. Pat. No. 4,567,746 and which may incorporate the transfer systems described above. This patent shows tooling lay-outs which may operate on stock material moving either from the front to the rear of the press or from side to side through the press. For example, the lay-out shown in FIG. 12 of this patent shows the material being fed from the front to the rear of the press with the first stations located over the stock material at the center of the press and the second stations located to either side of the stock material such that the transfer mechanism transfers the preformed shells sideways to the second stations.
In the lay-out shown in FIG. 13 of the '746 patent, the stock material is transferred from side to side through the press and the first stations are located over the stock material near a front portion of the press and the second stations are located adjacent to the stock material near a rear portion of the press. The tooling lay-outs for the above presses are arranged such that after passing through the first stations the scrap stock material remaining from the formation of the shell preforms is passed out of the press into a suitable chopper. It should be noted that the tooling is arranged such that after passing the first stage tooling, the web of scrap material will pass out of the press without intersecting the second tooling such that the web does not interfere with the transfer of the shell preforms or the operation of the tooling at the second station. As a result of this constraint on the tooling arrangement, the width of stock material available for a given press bed size is limited by the need to provide sufficient room for the second tooling and for removal of the scrap web, and thus the entire working area of the press bed is not utilized to its fullest potential.
In order to increase the output rate of the above-described press lay-outs, either the operating speed of the press must be increased such that more shells may be produced per unit of time from a given size of stock material, or the bed size of the press must be increased to accommodate a larger width of stock material and additional tooling stations, with consequent larger tooling.
It can be seen, therefore, that a tooling lay-out for a two-stage press is needed wherein the area of the press bed is fully utilized such that the number of shells produced per press stroke is maximized. Further, a tooling lay-out is needed for maximizing the output of the press while efficiently removing scrap metal, so as not to interfere with the transfer of shell preforms or the operation of the second shell forming stations.